Manganese (Mn) is a well-known neurotoxicant; however, the biochemical mechanisms contributing to its neurotoxicity are not well characterized. Both in vitro and in vivo studies will be conducted in order to investigate potential molecular mechanisms that may underlie the development and progression of Mn-induced neurotoxicity. These studies will examine if and how Mn disrupts cellular regulatory events, in particular, if one mechanism contributing to Mr-induced neurotoxicity is alterations in iron (Fe) homeostasis. The in vitro studies (Study I) will examine the effects of Mn on Fe homeostasis in primary oligodendrocyte, astrocyte, dopaminergic, and GABAergic neuronal cultures. Following exposure to Mn, the binding activity of the Iron Regulatory Proteins (IRPs) to the mRNA of transferrin receptor, m-aconitase, and ferritin will be examined; furthermore, the effect of potential changes in IRP binding activity on the translation of these proteins will be determined. As Fe is a redox active metal, disruptions in Fe homeostasis caused by Mn may result in heightened oxidative stress, thus total cellular reactive oxygen species production (ROS) will also be measured. These in vitro studies will enable the characterization of changes in Fe regulation and ROS production in response to elevated Mn exposure. In addition to these studies, in vivo studies using a rat model (Study II) will be done in order to validate whether the effects of Mn exposure observed in vitro also occur in vivo. Following 8 weeks of chronic exposure, the effects of elevated Mn on Fe homeostasis and ROS production will be evaluated in the frontal cortex, cerebellum, striatum, and thalamus. The information provided by these in vitro and in vivo studies will lend insight into new strategies for the prevention and treatment of Mn-induced neurotoxicity.